1. Field of the Invention
Method for the visual inspection of the reproduction quality of drawing elements and elements for the execution of the method.
The invention relates to a method for the visual inspection of the reproduction quality of drawing elements which are exposed by means of a cathode ray tube on light-sensitive photo meterial and also relates to elements for the execution of this method.
2. Technical Field
The invention relates to the field of type-setting technology, particularly to the field of electronic photocomposition for the production of printed products.
3. Description of the Prior Art
The employment of a cathode ray tube for the production of printing masters is presently encountered, for example, in the production of film setting, in plotters and in facsimile teletransmission of printing masters, for example, newspaper pages via telephone lines. Whole-page exposure of news print photo paper or directly on printing plates is, for example, a further use area of the cathode ray tube. The production of type matter in a photographic manner is thereby enjoying greater and greater acceptance and significance in the graphic industry. It may be presently assumed that lead composition will be successively replaced by film setting. In addition to the economical and technological advantages of film setting, however, film setting is burdened with the problem of quality protection.
The following elements are currently used in cathode ray film setting:
Font storage on a magnetic core or semiconductor base for storing image information; light source in the form of a cathode ray tube with an extremely fine resolution density; optical element which images the characters produced on the cathode ray tube onto the photo material and cassettes for the acceptance of film or photo paper. Devices of this type are disclosed, for example, in the U.S. Pat. No. 3,305,841 or in the U.S. Pat. No. 3,688,033.
The blackening or density on film setting paper during composition should be so high that such high contrast arises between the drawing element and the paper white that a photographic exposure on a graphic film is therewith made possible.
One encounters two groups of deficiencies under the quality-determining features of the type reproduction. One group contains errors in the mechanical alignment and positioning of individual letters and entire lines. A second group comprises errors in the optical transmission, i.e., in the exposure and development of the test columns.
Belonging to this group are primarily the blackening or density, the change of line thickness and the type sharpness.
A change of stroke thickness is expressed therein that individual lines or entire groups of text appear thicker or thinner than the surrounding text. This is considered ugly by those active in the graphic field and also by laymen, since the overall impression of printed matter has a restless and untidy effect due to this. Moreover, the legibility of such a text is reduced, since the reader, when he encounters a fatter line, initially believes that he has encountered an intentional emphasis of the text.
Density and change of stroke thickness are two features which largely proceed in parallel, i.e., that a change of density can also be expected given a change of the stroke thickness.
Three methods have been hitherto known for the inspection of the said features:
1. The reading microscope method for the inspection of the change of stroke thickness; PA1 2. The densitometric method for the inspection of the density and of the change of stroke thickness; and PA1 3. The microdensitometric method for the inspection of the density and the change of stroke thickness.
In the reading microscope method, a microscope is employed which is equipped with an ocular screw micrometer. After locating a suitable measuring location, the stroke thickness can be read at the scale division in the ocular. Since the beginning and the end of the stroke to be measured cannot be precisely established on the paper column due to the lack of edge sharpness, this method is subject to a certain uncertainty in fixing the effective stroke thickness.
In the densitometric method, the degree of surface coverage of a raster field exposed on the film setter is measured for the inspection of the change of stroke thickness. When the individual points or lines of the raster field expand, then the degree of surface coverage increases, the field appears optically darker, and a higher measured value can be detected with the densitometer.
In the microdensitometric method, the density over the entire width of the stroke to be measured is continuously sensed with a measuring gap aperture of 0.5 through 5.mu. and is recorded in the function of the locus coordinates on a writing means connected for this purpose. The stroke thickness and density can then be measured or, respectively, read from the recorded density profile.
All three described methods have the advantage that precise measured values exist which are not subject to the subjectivity of the human eye. However, expensive measuring instruments which are difficult to manipulate are required for the inspection and the personnel in the graphics trade is not trained for their proper operation. A further disadvantage, particularly in the first and third methods, is the enormous time outlay which is required for the measuring process.